As shown in FIG. 6, a decanter-type centrifugal separator 51 has a hollow bowl 54 and a screw conveyor 55 disposed inside the bowl 54 coaxially therewith. The separator 51 is configured such that where the bowl 54 and the screw conveyor 55 are rotated at a high speed, raw liquid to be processed that is introduced from a supply pipe 52 for raw liquid to be processed into the bowl 54 is separated by a centrifugal force and the separated fractions are discharged separately from each other.
More specifically, bowl hubs 56F, 56R installed at both ends of the bowl 54 are supported by bearings (bowl hub bearings 57F, 57R) that are fixed at the outer circumferential side, and the bowl is configured to rotate at a high speed upon receiving a rotational drive force from a drive means (not shown in the figure).
Meanwhile, the screw conveyor 55 is constituted by a conveyor hub 58 and a spiral flight 59 attached to the outer circumferential surface thereof. The two ends of the conveyor hub 58 are supported by conveyor hub bearings 60F, 60R, and the screw conveyor 55 is configured to be rotated at a speed different from that of the bowl 54 by a rotational drive force transmitted from a drive means via a differential gear 61. The conveyor hub bearings 60F, 60R supporting the screw conveyor 55 are disposed between the outer circumferential surfaces of the inner shafts 62F, 62R of the bowl hubs 56F, 56R that protrude into the bowl 54 and the inner circumferential surface of the conveyor hub 58 positioned radially outside thereof.
Ball bearings in which a plurality of balls is held between a track ring on the outer circumferential side and a track ring on the inner circumferential side are most often used as the bowl hub bearings 57F, 57R and the conveyor hub bearings 60F, 60R, and like other bearings (roller bearings or sliding bearings), they require lubricant (grease or the like) to be supplied therein after each predetermined period (for example, 3 months).
Since the bowl hub bearings 57F, 57R are disposed outside the bowl 54, as shown in the figure, a path for supplying the lubricant to the bowl hub bearings 57F, 57R is easily ensured, regardless of whether or not the separator is operated (the bowl 54 and the screw conveyor 55 rotate). Meanwhile, since the conveyor hub bearings 60F, 60R are disposed inside the bowl 54, it is very difficult to ensure a path by which the lubricant can be supplied to the conveyor hub bearings 60F, 60R during the operation.
Therefore, in the conventional decanter-type centrifugal separator 51 such as shown in FIG. 6, when the lubricant is supplied to the conveyor hub bearings 60F, 60R, it is necessary to stop the operation temporarily, stop the rotation of the bowl 54 and the screw conveyor 55, and then supply the lubricant.